This invention relates to a new process for the preparation of a formed iron catalyst by partial oxidation at the surface of iron or iron alloys in the form of shavings, granulates, or other particulate form, followed by reduction by hydrogenation. This invention further relates to a process for the preparation of primary amines, in particular hexamethylenediamine, by catalytic hydrogenation of the corresponding nitriles using iron catalysts prepared by this method.
It has long been known that iron catalysts can be used for the hydrogenation of nitriles, particularly adiponitriles, to the corresponding amines. Thus, German Patentschrift 848,654 discloses a process for hydrogenating adiponitrile using an iron catalyst which has been precipitated on pumice stone and reduced at an elevated temperature. According to German Offenlegungsschrift 2,429,293, a catalyst can be prepared by melting a Swedish magnetite ore at 1590.degree. C. After the molten iron oxide solidifies, the solid mass can be reduced in size and the resultant granulate reduced with hydrogen to yield a catalyst suitable for the hydrogenation of adiponitrile. The process for the hydrogenation of adiponitrile disclosed in German Auslegeschrift 2,034,380 also uses an iron catalyst that is prepared by reduction of a particulate iron oxide, for example, an iron ore occurring naturally in Labrador.
European Patent Application 101,584 proposes a method for hydrogenating adiponitrile using a formed iron catalyst mass containing metallic iron particles, which are obtained from anisometric iron oxide particles by hydrogen reduction. The process described for preparing the iron catalyst is relatively complicated, however, and the breakdown of the pieces obtained by compression of iron particles leads to a troublesome pressure increase when hydrogenation is carried out continuously.
It was, therefore, an object of the present invention to provide a simple process for the hydrogenation of nitriles, as well as to provide a catalyst for such a process. In particular, an object of the invention was to obtain a catalyst that could be prepared by a simple method from virtually any type of iron or iron alloy and that would combine the advantages of high activity with long service life. In addition, the difficult process of shaping the catalyst was to be avoided by using metallic iron in the form of particles suitable for heterogeneous catalytic processes.
The objects of the invention are accomplished by the processes described below for the preparation of an iron catalyst and for the preparation of primary amines by hydrogenating the corresponding nitriles in the presence of the catalyst.